When grub loads hit the "e" key to edit the entry to boot Ubuntu. Then scroll down to the linux line and remove the words quiet and splash. Then put nomodeset in where quiet and splash used to be.
Then hit ctrl X to boot. This will allow you to boot with nomodeset; and removing quiet and splash will allow you to see what is going on as the system boots.
This will only affect the current boot and will not make any permanent changes to the way Ubuntu boots.
Then try installing the nvidia driver from the Ubuntu repos and see if you can then boot to the desktop with the nvidia driver installed.